The belt driven data tape cartridge of Von Behren, U.S. Pat. No. 3,692,255 has become a standard interface with computers where rapid acceleration and deceleration of the tape are required. In these reel-to-reel tape cartridges, an elastic driving belt extends along a belt path around corner guide rollers positioned adjacent the tape reels, contacts the tape on the reels, and drives the tape from reel to reel. A tape path extends between the reels and along one edge of the cartridge across a cutaway portion providing access to the tape by a transducer such as a magnetic read/write head mechanism which is a part of a tape drive which receives the cartridge. The tape path is defined by a guide pin, a pair of tape guides, and in some cartridges, a pair of tape wrap pins, as originally disclosed in U.S. Pat. No. 4,221,348 to Moeller. One tape wrap pin is positioned between each reel and the adjacent tape guide to deflect the tape from a straight line path between the tape supply on the reel and the tape guide. This increases the frictional coupling between the tape and the tape wrap pin as the amount of tape wound on the reel increases and helps to maintain constant tape tension at the magnetic head.
In office environments, the noise levels that can be produced by tape cartridge operation are a serious problem. In addition to the aesthetic desirability of reducing noise, belt driven tape cartridges must meet ANSI and ISO noise standards.
Belt driven tape cartridges must meet minimum tape tension specifications while simultaneously maintaining maximum drive force specifications. The tape tension must not fall below a certain level as the tape passes from reel to reel or contact between the read/write head and the tape will be insufficient. The minimum achievable tape tension should be as high as possible to improve cartridge operation. Similarly, the maximum required drive force, the force applied to the cartridge drive roller, should be as low as possible to enhance cartridge operation within the power limitations of the drive motor which prevent the drive force from exceeding a particular level. These parameters are dependent on friction within the cartridge, therefore all friction sources must be controlled. Unlike other interfaces within the cartridge, such as the tape/tape guide interface, the interface between the drive roller and its pivot pin, and the interface between the reel and its pivot pin, where friction is to be minimized, corner guide roller friction is required to generate tape tension. Unless this friction is maintained within specific ranges, the tape cartridge will not perform properly.
Data tape cartridge rotating components can operate within various lubrication schemes in the interface between the guide roller and the pivot pin. At one extreme is a full film lubrication design, in which a relatively thick layer of lubricant resides between the guide roller and its pivot pin. The friction depends on the viscous properties of the lubricant which can push out of the interface between the guide roller and the pivot pin. A dry scheme involves no lubricant between the guide roller and its pivot pin. Between these two extremes are the boundary lubrication and the mixed lubrication designs. In mixed lubrication, regions of contact between the roller and its pivot pin are interspersed with regions of a relatively thick layer of lubricant. In a boundary lubrication scheme, a uniformly thin, "carpet" layer of lubricant resides between the roller and its guide pin. This permits smooth contact between the roller and pin that is governed by the respective surface characteristics of the parts. The guide roller-pivot pin interfaces in known cartridges typically operate in the mixed lubrication regime. Therefore, the surface texture, clearance, and lubricant significantly affect friction generation. Also, a smooth interface with regular asperities reduces vibrations which reduces operating noise levels.
One method for generating tape tension is to apply drag to the driving belt. Early attempts at directly contacting the driving belt with some form of brake to apply sliding friction, such as disclosed in U.S. Pat. No. 3,620,473, were found to unduly wear the belt and create debris within the cartridge. The difficulty in obtaining sufficiently controllable friction between a corner guide roller and its roller pivot pin while maintaining smooth rolling of the roller is documented in U.S. Pat. No. 4,102,516. The apparatus of this patent addresses this problem by using a biased washer to contact the guide roller hub and apply drag to the roller. However, this requires adding extra components to the tape cartridge, thereby increasing the cartridge complexity and presenting manufacturing difficulties. Additionally, the biasing characteristics of the washer can vary unacceptably over time, and drop tests have shown that this cartridge is not durable.
U.S. Pat. No. 4,474,342, discloses a belt driven tape cartridge in which one of the belt guide rollers is supported by a spring which biases the guide roller in a direction to lengthen the driving belt path to apply tension to the driving belt. However, this cartridge has a relatively complex driving belt path. Moreover, the spring introduces an additional subassembly into the tape cartridge and the biasing characteristics of the spring can vary unacceptably over time.
One current method for applying drag to the driving belt is to texture the bore of the guide roller to create friction between the guide roller and its pivot pin. The texture is created by sand or glass bead blasting (hereinafter sandblasting) a molding core pin and then molding the guide roller around the core pin. In this sandblasting technique, grains of abrasive particles such as silicon carbide or aluminum oxide are ejected from a nozzle and impinge on the surface of the molding core pin at a predetermined angle. The characteristics of the resulting texture are a function of the size, shape, and composition of the abrasive particles, the angle at which the particles strike the core pin surface, and the average velocity of the particles when they strike the core pin surface. The average velocity is directly determined by the nozzle pressure. Because the particles are harder than the surface being treated, the treated core pin surface is made up of many small and irregularly shaped pockets or pits, The resulting texture includes numerous random, uncontrolled, unrepeatable impressions caused by the impact of the individual abrasive particles. Also, as the guide roller is ejected from its molding core pin during manufacture, drag patterns are produced which alter the surface finish. Although this method can produce a desirable level of guide roller friction, the core pins and the resulting guide rollers formed using this process are irregular and the patterns formed thereon are not repeatable from roller to roller. Moreover, the degree of asperity contact, which controls friction, is difficult to quantify. As a result, cartridges using rollers formed by this method have a high variability in tape tensioning in their operation.
Omachi, Japanese Kokai No. 63-114471 discloses guide rollers with oil retaining grooves on the inner wall. The oil retaining grooves prevent lubricating oil from flowing in the direction of guide roller rotation and can reduce friction but are not disclosed as controlling the amount of friction or defining a range of friction between the guide roller and its pivot pin. Thus, the grooves do not necessarily enable the roller to yield constant repeatable results pass-to-pass within a cartridge or from cartridge-to-cartridge. They do not enable the roller to yield constant repeatable results pass-to-pass within a cartridge and from cartridge-to-cartridge.
None of these existing tape cartridges includes a simple yet consistent way to control drag on the driving belt to reduce the variability in the mechanical operation of the cartridge. None of the known guide rollers has a controlled surface texture which can control and define a desirable range of friction between the guide roller and its pivot pin. None of the references discloses repeatable roller operation and operating in a boundary lubrication scheme. None of the references teaches using a predetermined amount of friction which yields constant repeatable results pass-to-pass within a cartridge and from cartridge-to-cartridge. Nor does any reference disclose a corner guide roller which, in addition to controlling friction, controls and limits cartridge vibrations and acoustic noise.
There is a need for a belt driven tape cartridge in which the drag is less dependent on the tape speed than in existing cartridges to achieve higher minimum tape tension at low tape speeds as well as lower maximum drive force at high tape speeds. There is also a need for a tape cartridge in which there is low vibration at the guide roller-pivot pin interface to produce low noise levels during operation. There is also a need for a method of manufacturing guide rollers in which the characteristics of the rollers are highly repeatable and remain consistent from roller to roller.